1. Field of the Invention
This invention relates to graft polymers of the ABS type which are produced in emulsion, and to thermoplastic moulding compositions which are based thereon and which exhibit a very considerably increased notched bar impact strength compared with known ABS moulding compositions and which at the same time exhibit high hardness values or high modulus values and good thermoplastic processability.
2. Description of the Prior Art
ABS moulding compositions are two-phase synthetic materials comprising:
I: a thermoplastic copolymer of styrene and acrylonitrile, in which the styrene may be completely or partially replaced by .alpha.-methyl styrene or methyl methacrylate; this copolymer, which is also termed SAN resin or matrix resin, forms the external phase; PA1 II: at least one graft polymer, which has been produced by a graft reaction of one or more of the monomers cited in I. on to a butadiene homo- or copolymer ("graft base"). This graft polymer ("elastomer phase" or "graft rubber") forms the disperse phase in the matrix resin. PA1 I) at least one graft polymer, obtained by the emulsion polymerisation of styrene and acrylonitrile in a weight ratio of 90:10 to 50:50, wherein styrene and/or acrylonitrile can be completely or partially replaced by .alpha.-methylstyrene, methyl methacrylate or N-phenylmaleinimide, in the presence of at least two butadiene polymer latices of type (A) and (B), which each contain 0 to 50% by weight of a further copolymerised vinyl monomer and wherein the weight ratio of the monomers used to the butadiene polymers used is 20:80 to 80:20, preferably 30:70 to 75:25, and PA1 II) at least one copolymer of styrene and acrylonitrile in a weight ratio of 90:10 to 50:50, wherein styrene and/or acrylonitrile can be completely or partially replaced by .alpha.-methylstyrene, methyl methacrylate or N-phenylmaleinimide, PA1 i) butadiene polymer latex (A) has a particle diameter d.sub.50 .ltoreq.320 nm, preferably 260 to 310 nm, a particle size distribution range (measured as d.sub.90 -d.sub.10 from the integral particle size distribution) from 30 to 100 nm, preferably from 40 to 80 nm, and a gel content .ltoreq.70% by weight, preferably 40 to 65% by weight, and butadiene polymer latex (B) has a particle diameter d.sub.50 .ltoreq.370 nm, preferably 380 to 450 nm, a particle size distribution range (measured as d.sub.90 -d.sub.10 from the integral particle size distribution) from 50 to 500 nm, preferably from 100 to 400 nm, and a gel content .ltoreq.70% by weight, preferably 75 to 90% by weight, PA1 ii) at least one compound of general formula R ##STR1## wherein R'=C.sub.2 H.sub.5, C.sub.3 H.sub.7, C.sub.4 H.sub.9, is used in amounts of 1 to 5% by weight, preferably 1.5 to 3% by weight (with respect to the monomers in each case) as a radical former for the production of the graft polymer, and PA1 iii) the weight ratio of radical former R:emulsifier which is used in the graft polymerisation is 1:1 to 1:5, preferably 1:1 to 1:3. PA1 70 to 99 mole % of the 4,4'-diamino isomer, PA1 1 to 30 mole % of the 2,4'-diamino isomer, PA1 0 to 2 mole % of the 2,2'-diamino isomer, and
For the same matrix, the toughness of an ABS moulding composition is substantially determined by the graft rubber contained therein. However, the toughness which can be obtained, with the requisite reliability, using customary ABS moulding compositions is not always sufficient for highly stressed mouldings, or high toughness values are obtained, but to the detriment of other properties of the mouldings.
There is therefore a need for highly effective graft rubbers, based on which ABS moulding compositions having a very high toughness can be produced without their other properties being altered in a negative sense.
It has now been found that with the simultaneous use of a special mixture of at least two accurately defined rubber latices and defined added amounts of special radical initiator compounds and emulsifiers during the production of the graft rubber, and preferably with the maintenance of special reaction conditions, ABS moulding compositions which have very high impact toughness values can be obtained.
The use of rubber latex mixtures in the production of graft rubbers for ABS moulding compositions is in fact known, although the quality requirements are not fulfilled.
Thus, for example, tough ABS moulding compositions which exhibit good processability are known from DE-AS 1 813 719; these are obtained by the single-stage emulsion graft polymerisation, which proceeds under pressure, of 75 to 90 parts by weight of a monomer mixture on to 10 to 25 parts by weight of a mixture of two rubber latices, one of which is a pure polybutadiene and the other is an SBR latex with a styrene content &lt;50% and with a defined particle size.
U.S. Pat. No. 3,509,238 describes ABS products which are produced using two graft polymers, one of which is weakly grafted, the other of which is strongly grafted. These products have unsatisfactory properties at low temperatures, however.
U.S. Pat. No. 3,928,494 describes ABS products comprising two graft polymers comprising different degrees of grafting, in which the more weakly grafted, finely divided material is layered together during spray-drying or during coagulation to form particle aggregates. Aggregates of this type constitute loosely bound formations which are torn apart again under the action of high temperatures and shear forces, such as those which can occur in injection moulding processing for example, and do not then result in satisfactory product toughnesses.
EP-A 116 330 describes ABS moulding compositions based on two different butadiene polymers, with a special grafting site spacing of the graft polymers produced from the butadiene polymers. These products in fact exhibit good toughness at room temperature, but their hardness values and their thermoplastic flowability are not adequate for severe demands.